An experimental study has been performed in order to investigate the relationship between theextensional viscosity of polymers and the turbulent drag reduction. Polyethyleneoxide as flexiblepolymer and hydroxypropyl cellulose as rigid rod-like polymer were added to the two-dimensionalturbulent flow that was visualized by the interference pattern of a flowing soap film and analyzed byan originally developed single-image analysis. The power spectra of interference images wereobtained, which is related to the water layer fluctuations in turbulence. The power spectra show ascaling behavior and the power components give the information of drag reduction. It was found fromthese results that the energy transfer mechanisms are different in streamwise and normal directions. Inthe normal direction, the energy transfer is prohibited by the orientation of polymers, while the energytransfer in the streamwise direction is prohibited by extensional viscosity of polymers. In order to getthe precise information of frequency fluctuation in the streamwise direction that is related to theextensional viscosity, a wavelet-coefficient of interference images in the streamwise direction wascalculated. The characteristic correlation scales were observed as a periodic structure inwavelet-coefficients, which was changed by the concentration of polymers. These scales may relateto the energy transfer in turbulence.
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